Molded closure for a liquid container

ABSTRACT

A molded closure for a liquid container comprising a thermoplastic elastomer and a blowing agent. The molded closure is particularly suitable for use as a synthetic wine cork in a wine bottle. The molded closure does not permit passage of oxygen into the container, does not absorb oxygen from the contents of the container, can be removed from the container using a corkscrew without significant expansion, crumbling or disintegration, does not significantly taint a liquid in the container, permits the container to be placed horizontally immediately after insertion of the molded closure, and can permanently retain printed matter on its surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/058,914, filed May 5, 1993.

TECHNICAL FIELD

The present invention relates to molded closures for liquid containersand to compositions and methods for making such closures. In one aspect,the present invention relates to a composition for producing moldedstoppers for bottles, particularly wine bottles, from a thermoplasticelastomer mixed with a blowing agent, and products from such acomposition. In other aspects, the invention relates to a method formaking molded closures such as wine bottle corks and a method of makinga stoppered wine bottle.

BACKGROUND OF THE INVENTION

The most commonly used material for making stopper-type bottle closuresis natural cork. There are, however, significant disadvantages to usingcork in the manufacture and marketing of bottle closures. Cork hasvariable properties with respect to color, drying, shrinkage orexpansion, crumbling, sticking to containers and seal formation. Thesefeatures are generally unsatisfactory in terms of production andconsumer costs as well as product performance. In the case of wineclosures, cork may also impart an odor to the product, causing it to berejected by consumers. In addition, nearly 10% of bottled wine isdiscarded because of unpredictable contamination by mold from naturalcork. Further, the use of cork for producing bottle closures is becomingincreasingly expensive as the supply of trees from which cork isobtained rapidly diminishes.

Numerous attempts have been made to develop alternatives to natural corkbottle stoppers. Among these, screw top closures for wine containershave been found largely unsuitable because they do not provide theappearance, ceremony or romance that surrounds traditional cork wineclosures. A number of synthetic cork closures have also been developed.In particular, recent efforts to develop closures from injection moldedfoam thermoplastics have encountered numerous pitfalls, particularly interms of production costs, product performance, and consumer acceptance.Some of these closures have exhibited a tendency to noticeably taint theproduct and/or offer low resistance to oxygen permeation into thecontainer. In addition, synthetic closures from foam thermoplastics havegenerally exhibited poor uniformity in terms of size, shape, weight, andother features important to production, marketing, and performance.

In a particular case of injection molding of foam thermoplastic closuresfor liquid containers, thermoplastic compositions are injected intorelatively cool molds, leading to the formation of a dense outer "skin"at the surface of the closure and a porous, foam-like interior. Thecomposition of the closure and the structural relationship between theouter skin and porous core of the closure may be critical to the sealingcapabilities of the finished closure. Other foam thermoplastic closureshave suffered problems due to wrinkling of the outer skin layer, whichcan produce leakage fissures between the closure and container. Otherprior art closures have different sealing problems, for example, failingto quickly return to normal size after compression, such that reliableseal formation requires containers to be kept in an upright position foran extended period after insertion of the closure. Further, prior artclosures are unable to significantly retain printed matter for asignificant period of time.

U.S. Pat. No. 4,363,849 discloses the production of thermoplasticclosures having a natural cork-like appearance. Special moldingapparatus are used, however, and it is necessary to gradually releasethe air in the cold molding cavity that is displaced by the injectedthermoplastic resinous material by means of controlled minimum ventingor other means in order to maintain a heightened pressure, for exampleabout 16,000 psi, within the mold. U.S. Pat. No. 4,188,457 discloses athermoplastic composition that is also used to form closures for winebottles. The thermoplastic composition includes sulfur dioxide andwater, and the sulfur dioxide is said to act as an oxygen scavenger.This method is undesirable, however, because the sulfur dioxide or themetabisulphite from which it is produced may taint the liquid in theclosure.

OBJECTS AND SUMMARY OF THE INVENTION

A general object of the present invention is to provide a molded closurefor liquid containers comprising a thermoplastic elastomer ("TPE") and ablowing agent that, when fitted into a liquid container, offers highresistance to oxygen permeation and produces little or no producttainting. The molded closure can also be produced for non-liquidcontainers.

Another object of the present invention is to provide a composition thatcan be readily fabricated into suitable closures for liquid containers,for example, wine bottles.

A further object of the present invention is to provide a compositionfor manufacturing closures for liquid containers that have essentiallyall of the desirable qualities of natural cork, but preferably none ofthe undesirable features.

Yet another object of the present invention is to provide processes forinjection molding closures for liquid containers.

Still another object of the present invention is to provide a novelcomposition and process for fabricating a closure that reliably sealsliquid containers immediately upon insertion, and/or that is able toretain printed matter.

The molded closure of the present invention is preferably molded in theshape of a cork sized to fit a wine bottle. It has substantialuniformity of size, shape and weight and is aesthetically pleasing. Itsappearance is distinctive from the look of natural cork by virtue of thepresent invention's artificial coloring, marbled surface texture, andability to have a symbol embossed on its surface, preferably at one orboth of its ends. In addition, the closure may be readily inserted intoliquid containers using standard bottling equipment, and is easilyremoved using a traditional corkscrew without sticking, crumbling orsubsequent expansion. Because the molded closure of the invention doesnot expand upon removal, it may be re-inserted into the liquidcontainer, thereby reclosing the container when it is not fully emptied.The molded closure may also be contacted with liquid contents in thecontainer immediately after insertion, thereby removing the need for awaiting period to allow for formation of a proper seal between themolded closure and the container before the container is placedhorizontally. The molded closure can also permanently retain printedmatter.

These and other aspects of the present invention will become evidentupon reference to the following detailed description and attacheddrawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a molded closure suitable for a wine bottle, the moldedclosure evidencing a marbled surface texture, an embossed symbol on anend, printing on its side, and a radius at its edge.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided a moldedclosure for liquid containers that can function as a suitablereplacement for natural cork, wherein it is possible to control thesize, shape, surface texture, surface lubricity, resilience, elasticity,density distribution, and aesthetic appearance of the molded closure.

Accordingly, the present invention features a molded closure for aliquid container, preferably a wine bottle, comprising a TPE and ablowing agent in a ratio suitable to provide a molded closure able toclose a bottle of wine, thereby preventing spillage, and able to preventpassage of oxygen from the atmosphere to the wine, while simultaneouslynot substantially absorbing oxygen from the wine or the air space withinthe wine bottle between the molded closure and the wine. The moldedclosure has the ability to be removed with a corkscrew withoutsubstantial expansion, crumbling or disintegration (such expansion,crumbling or disintegration either causes the wine to become generallyunpalatable and/or render the molded closure unusable).

It is possible to print on the molded closure, including on the surfaceof the molded closure that contacts the container, and the container canbe placed on its side immediately after the molded closure is insertedinto the container. The molded closure also has the ability to be usedover an extended period (suitable for the wine to properly age to reachan appropriate drinkability, which can be about two years or more), andthe ability to resist solvation in alcohol, acid or base, therebykeeping the wine free from tainting. Preferably, the molded closurefurther comprises one or more of a lubricant, a coloring agent, afiller, or other additives that can improve the performance and/orproducibility of the closures. The molded closure does not, for example,include an oxygen scavenger, such as sulfur dioxide, which has been usedin the past to increase the impermeability of synthetic corks, but whichcan taint the wine.

In another aspect of the invention, the molded closure is formed from acomposition comprising one or more TPEs and one or more blowing agents.The durometer measurement of the molded closure, which is effectively anindirect measure of the hardness of the TPE used to make the moldedclosure, is generally from about 65A to about 90A, typically from about70A to about 85A, and preferably from about 71A or 75A to about 80A. TheTPE generally comprises from about 70% to about 97% of the composition,typically from about 80% to about 95%, and preferably from about 90% toabout 95% of the composition (unless otherwise noted, all percentagesherein are by volume). The TPE exhibits little or no interaction with,or tainting of, liquids such as wine. The TPE also has a suitable forceof compression for improved sealability and long service life. The TPEis easily processed, enabling fast cycle times and high productionrates. Further, selected TPEs meet FDA requirements for indirect foodadditives intended to come in contact with food.

In a preferred embodiment, the TPE comprises a styrenic block copolymer,and further preferably comprises one or more of astyrene-ethylene-butylene-styrene copolymer ("SEBS"), astyrene-ethylene-butylene copolymer, a styrene-butadiene-styrenecopolymer, a styrene-butadiene copolymer, a styrene-isoprene-styrenecopolymer, a styrene-isoprene copolymer, astyrene-ethylene-propylene-styrene copolymer, and astyrene-ethylene-propylene copolymer. The inclusion of a styrenic blockcopolymer, and particularly SEBS, is especially advantageous in themolded closure (especially when the molded closure is a wine cork)because such copolymers provide superior properties to the moldedclosure when compared to other TPEs. Many of these copolymers areavailable under the tradename KRATON®. In a still further preferredembodiment, the styrenic block copolymer is SEBS. Examples of such SEBScopolymers include J-VON®, DYNAFLEX GS6771-000 AND DYNAFLEX GX6768-1000,which possess desirable ozone and heat resistance for a long servicelife. In addition, such SEBS copolymers are resistant to water, bases,acids, and alcohol. J-VON® is commercially available from J. Von Ltd.Partnership, Leominster, Mass.; DYNAFLEX GS6771-000 and GX6768-1000 areavailable from CC&P, Portland, Oreg.

The blowing agent generally comprises greater than 1% of thecomposition, and typically comprises a range that includes at leastabout 1.3%, 1.5% or 2.0% of the composition, and less than about 9.0%,5.0%, 4.0% or 3.0% of the composition. Preferably, the blowing agentcomprises from about 1.3% to about 3% of the composition, typically fromabout 1.5% to about 2.5%, and preferably about 2% of the composition.The precise amount of blowing agent used may be determined by oneskilled in the art of taking into account the precise polymer, blowingagent, and other ingredients used, as well as the molding conditions.The use of too much blowing agent will generally result in a moldedclosure that has excessively large cells in its interior, thus causingthe molded closure to be overly spongy and potentially inconsistentduring production. The use of too little blowing agent will generallyresult in a molded closure that does not have enough cells orinadequately sized cells. Such a molded closure can be too hard forroutine removal using a corkscrew, among other problems.

In a preferred embodiment, the blowing agent is Spectratech FM1150H,which is commercially available from Quantum Chemical Corp., USIDivision, Cincinnati, Ohio. Spectratech™ FM1150H is a polyolefin-basedcompound consisting of a low-density polyethylene based endothermic foamconcentrate, comprising 50% of resin of the formula CH₃ --(CH₂)_(n)--CH₃ and 50% of a combination of sodium bicarbonate (NaHCO₃) and citricacid. The beneficial qualities of Spectratech™ FM 1150H include rapiddegassing, improved cycle times, improved density distribution, andsuperior surfaces for molded articles. Other suitable blowing agentssuch as azodicarbonamide, ozodecarbonoxide, and sodium bicarbonate alsomay be used. Still other blowing agents may be used without departingfrom the spirit and scope of the present invention.

In another embodiment, one or more fillers may be used in combinationwith the TPE and other added materials. For example, the filler maycomprise calcium carbonate. If such a filler is used, it comprises up toabout 20% or more of the composition, but preferably up to about 5% ofthe composition. Using such a filler can economize materialexpenditures. Other filler materials are apparent to those skilled inthe art.

In another embodiment of the present invention, powder or liquidpigments are added to the mixture of TPE and other materials. The powderor liquid pigments generally comprise less than about 1% of the totalcomposition. Preferably, the pigment is pre-blended with a thermoplasticresinous material such as polypropylene, and/or a portion of the TPE,before its addition to the main feedstock of TPE and other materials.

In a preferred embodiment, the composition comprises about 96% TPE,about 2% blowing agent, about 2% low density polypropylene, and a minorpercentage of a desired pigment. In a further preferred embodiment, thepigment, the polypropylene and about 2% of the TPE are pre-blended, thenintroduced as a homogeneous mixture to the remaining TPE and blowingagent. In an alternative preferred embodiment, wherein the compositionfurther comprises a filler, the composition comprises from about 75% toabout 95% TPE, from about 1.5% to about 2.5% blowing agent, and up toabout 20% filler.

In yet another preferred embodiment, a lubricant such as a fatty acid, asilicone, alcohol or water (including mineral water) is added before orafter the molding, which may ease insertion of the molded closure into acontainer. Preferably, the lubricant is a fatty acid, and comprises lessthan about 0.5% of the total composition.

In another aspect, the present invention provides a molded closure thathas a rounded edge, or radius, which is preferably convex. Preferably,the radius is on both edges (i.e., the top and bottom) of the closure.This aspect of the invention is preferably used with molded closurescomprising a TPE, but is also suitable for use with molded closuresproduced from traditional thermoplastic resins that are not TPEs. Such aradius allows easier and more effective insertion of the molded closureinto a container (particularly a wine bottle), allows the molded closureto maintain a more uniform exterior surface when the molded closure isplaced within a container, and is believed to assist in the ability ofthe molded closure to permit a container to be placed on its sidesubstantially immediately after insertion of the molded closure.

It is a feature of the present invention that the molded closure canpermanently retain printed matter on the surface of the molded closurethat contacts the container. The surface of a molded closure istypically very slick and therefore unable to effectively receive or toretain such printed matter. In order to retain the printed matter, thecompound is preferably a TPE, preferably a styrene block copolymer, andfurther preferably an SEBS copolymer, although a thermoplastic resin mayalso be used for this embodiment of the invention. Further, the moldedclosure, subsequent to molding, is preferably subjected to a treatmentto prepare the surface for printing. The treatment comprises subjectingthe molded closure to high intensity electromagnetic radiation, andpreferably in the visible light range or near the visible light range(e.g., U.V. light). One example of such a treatment is known as a coronapre-treatment, which is a standard treatment in the printing industry.The treatment is preferably performed prior to printing, but can beperformed after printing.

It is yet another feature of the present invention that a container,such as a wine bottle, can be placed horizontally generally within about4 hours, typically within about 1 hour, and preferably substantiallyimmediately after receiving a molded closure produced according to thepresent invention. It is believed that this property of the moldedclosure is attained because the inventive composition permits the moldedclosure to achieve an interior cell size that causes the molded closureto return to at least about 90% of its original diameter within about 4to about 5 seconds after being released from a compressed state. It isalso believed that the inclusion of a radius edge on the molded closureaids this property of the molded closure.

Accordingly, after the molded closure is compressed and inserted intothe container, the molded closure returns to approximately its normalsize within from about 4 to about 5 seconds, thereby allowing thecontainer to be immediately placed horizontally without spilling thecontents of the container and without interfering with the seal betweenthe molded closure and the container. For example, when the container isa wine bottle, it does not need a standing period before being racked.

In still another embodiment of the present invention, one or more othermaterials may also be added to the overall composition, includingchemical blowing agent activators and other additives that can improvethe producibility and/or performance of the closures. For example, ifdesired, a material can be added that can enhance the aroma and/orflavor of the liquid in the container.

It is a further feature of the present invention that the molded closuremay be created using standard injection molding procedures.

In one example of the molding process, the bulk of the materials of thecomposition are thoroughly mixed to provide a uniform feedstock. Thefeedstock is next processed to be suitable for injection into aninjection mold. In another vessel, pigment, polypropylene and a smallportion of the TPE (preferably SEBS compound) are mixed to homogeneity.The prepared feedstock and the pigment bearing mixture are then injectedinto the mold, generally over a period of from about 0.02 to about 6seconds, typically from about 0.03 to about 2 seconds, and preferablyfrom about 0.04 to 1 second. The mold has a desired shape, whichpreferably is the shape of a wine cork. The molding pressure isgenerally from about 200 psi to about 900 psi, typically from about 300psi to about 800 psi, and preferably from about 400 psi to about 700psi. The molding temperature is generally from about 300° F. to about550° F., typically from about 325° F. to about 425° F., and preferablyfrom about 350° F. to about 400° F., and further preferably about 375°F. The mixture is generally maintained in the mold from about 20 secondsto about 90 seconds, typically from about 30 seconds to about 80seconds, and preferably from about 35 seconds to about 60 seconds.Further preferably, the molding is performed as quickly as possible.Further, no special venting is required.

In a preferred embodiment, the composition is injected into the mold ata rate and temperature such that the softened or molten compositionrandomly coils about in the mold, much like a string being lowered intoa bottle, to produce visible random curling along the surface of themolded closure, as depicted in FIG. 1. In an alternative embodiment, thecomposition is injected at a rate and temperature such that randomcuring is avoided.

Further, the air in the mold at the beginning of a mold cycle ispreferably removed from the mold by means of a vacuum assist coordinatedwith the injection of the composition. The vacuum assist can be appliedfor about the last second of the injection period, or it may be firstapplied after the end of the injection period. Applying the vacuumassist too early in the injection period may result in overly large cellspaces within the molded closure, yielding an overly spongy product.Failure to use a vacuum assist may result in increased cycle times.

After a time period sufficient for the overall composition toeffectively harden within the mold, the mold is opened and the moldedclosure is removed.

Molding times, pressures, venting, cooling, vacuum assisting, productremoval, and other factors relevant to injection molding will be basedupon the precise combination of materials included in the overallcomposition, the type, size and shape of the mold, and other factorsapparent to those having ordinary skill in the art.

It is a feature of the present invention that the mold, preferably atone or both ends, can have embossed thereon a desired symbol, such as acrest of a wine cellar or lettering, and that such embossed symbol willbe imparted to the cork.

The present embodiments of this invention are to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes that come withinthe meaning and range of equivalency of the claims therefore areintended to be embraced therein.

What is claimed is:
 1. A molded closure for a liquid containercontaining wine comprising:(a) a thermoplastic elastomer comprising astyrene block copolymer, and (b) a blowing agent, wherein, uponinsertion of said molded closure into a container, said molded closuredoes not permit substantial passage of oxygen into the container, doesnot substantially absorb oxygen from the contents of the container, canbe removed from said container using a corkscrew without substantialexpansion, crumbling, or disintegration, does not substantially taintthe contents of said container, permits said container to be placedhorizontally substantially immediately after insertion of said moldedclosure into said container, and can permanently retain printed matteron a surface of said molded closure, wherein said thermoplasticelastomer comprises one or more of a styrene-ethylene-butylene-styrenecopolymer, styrene-butadiene-styrene copolymer, and astyrene-isoprene-styrene copolymer.